root/library/bdm/shared_ptr.h @ 570

/*!
  \file
  \brief BDM's own smart pointers.
  \author Vaclav Barta.

  -----------------------------------
  BDM++ - C++ library for Bayesian Decision Making under Uncertainty

  Using IT++ for numerical operations
  -----------------------------------
*/

#ifndef shared_ptr_h
#define shared_ptr_h

#include <limits.h>
#include <algorithm>
#include <stdexcept>
#include <string>
#include "bdmerror.h"

namespace bdm {

/*! \brief A naive implementation of roughly a subset of the std::tr1::shared_ptr spec

  Really just roughly - it ignores memory
  exceptions, for example; also note I didn't read the spec.

  The standard template would naturally be preferable, \b if it was
  included in the standard libraries of all supported compilers - but
  as of 2009, that's still a problem...
*/
template <typename T>
class shared_ptr {
        template<class U> friend class shared_ptr;

private:
        T *payload;
        unsigned *refCnt;

public:
        /*!
          \brief Default constructor

          Creates an empty shared_ptr - one that doesn't point anywhere.
        */
        shared_ptr() :
                        payload ( 0 ),
                        refCnt ( 0 ) {
        }

        /*! 
          Constructs a shared_ptr that owns the pointer p (unless p
          is NULL, in which case this constructor creates an empty
          shared_ptr). When p isn't null, it must have been alllocated
          by new!
        */
        shared_ptr ( T *p ) :
                        payload ( p ),
                        refCnt ( p ? new unsigned ( 1 ) : 0 ) {
        }

        /*!
          \brief Copy constructor

          If other is empty, constructs an empty shared_ptr; otherwise,
          constructs a shared_ptr that shares ownership with other.
        */
        shared_ptr ( const shared_ptr<T> &other ) :
                        payload ( other.payload ),
                        refCnt ( other.refCnt ) {
                add_ref();
        }

        /*!
          \brief Generalized copy

          Allows initialization of shared pointer of a base type from
          raw pointer to a derived type.

          If other is empty, constructs an empty shared_ptr; otherwise,
          constructs a shared_ptr that shares ownership with other.
        */
        template<typename U>
        shared_ptr ( const shared_ptr<U> &other ) :
                        payload ( other.payload ),
                        refCnt ( other.refCnt ) {
                add_ref();
        }

        /*!
          Destructor.
        */
        ~shared_ptr() {
                del_ref();
        }

        /*!
          \brief Assignment operator
        */
        shared_ptr<T> &operator= ( const shared_ptr<T> &other ) {
                other.add_ref();
                del_ref();

                payload = other.payload;
                refCnt = other.refCnt;

                return *this;
        }

        /*!
          Returns the stored pointer (which remains owned by this
          instance). For empty instances, this method returns NULL.
        */
        T *get() {
                return payload;
        }

        /*!
          Dereferences the stored pointer (which remains owned by
          this instance). This method may only be called when the
          stored pointer isn't NULL.
        */
        T *operator->() {
                bdm_assert_debug ( payload, "dereferencing NULL" );
                return payload;
        }

        //! Returns a reference to the object pointed to by the stored
        //! pointer. This method may only be called when the stored pointer
        //! isn't NULL.
        T &operator*() {
                bdm_assert_debug ( payload, "dereferencing NULL" );
                return *payload;
        }

        /*!
          Returns the stored pointer (which remains owned by this
          instance). For empty instances, this method returns NULL.
        */
        const T* get() const {
                return payload;
        }

        //! Returns the stored pointer (which remains owned by this
        //! instance). This method may only be called when the stored
        //! pointer isn't NULL.
        const T *operator->() const {
                bdm_assert_debug ( payload, "dereferencing NULL" );
                return payload;
        }

        //! Returns a reference to the object pointed to by the stored
        //! pointer. This method may only be called when the stored pointer
        //! isn't NULL.
        const T &operator*() const {
                bdm_assert_debug ( payload, "dereferencing NULL" );
                return *payload;
        }

        //! Returns use_count() == 1
        bool unique() const {
                return refCnt && ( *refCnt == 1 );
        }

        /*!
          Returns the number of shared_ptr instances (including
          this instance) that share ownership with this instance. For
          empty instances, this method returns 0.
        */
        long use_count() const {
                return refCnt ? *refCnt : 0;
        }

        /*!
          \brief Boolean cast

          This operator returns true if and only if the instance isn't empty.
        */
        operator bool() const {
                return !!payload;
        }

        /*!
          \brief const cast

          Shared pointer to T can be converted to shared pointer to
          const T, just like T * can be converted to T const *.
        */
        template<typename U>
        operator shared_ptr<const U>() const {
                shared_ptr<const U> cptr;               
                cptr.refCnt = refCnt;
                cptr.payload = payload;
                add_ref();
                return cptr;
        }

        /*!
          \brief Efficient swap for shared_ptr.
         */
        void swap ( shared_ptr &other ) {
                std::swap ( payload, other.payload );
                std::swap ( refCnt, other.refCnt );
        }

private:
        void add_ref() const {
                if ( refCnt ) {
                        if ( *refCnt == UINT_MAX ) {
                                throw std::overflow_error (
                                    std::string ( "Shared pointer has too many references." ) );
                        }

                        ++*refCnt;
                }
        }

        void del_ref() {
                if ( refCnt ) {
                        if ( ! ( --*refCnt ) ) {
                                delete payload;
                                delete refCnt;
                        }
                }
        }
};

//! Compare shared pointers 
template<typename T, typename U>
bool operator== ( shared_ptr<T> const &a, shared_ptr<U> const &b ) {
        return a.get() == b.get();
}

//! Compare shared pointers 
template<typename T, typename U>
bool operator!= ( shared_ptr<T> const &a, shared_ptr<U> const &b ) {
        return a.get() != b.get();
}

//! Compare shared pointers 
template<typename T, typename U>
bool operator< ( shared_ptr<T> const &a, shared_ptr<U> const &b ) {
        return a.get() < b.get();
}

/*! \brief A wrapper of shared_ptr which is never empty.

  T must have a default constructor.

  Note that shared_ptr's destructor isn't virtual - don't call delete
  on pointers to instances of this class.
 */
template <typename T>
class object_ptr : public shared_ptr<T>
{
public:
        /*!
          \brief Default constructor

          Calls T's default constructor.
        */
        object_ptr() : shared_ptr<T> ( new T() ) { }

        /*!
          \brief Upcast from shared_ptr<T> to object_ptr<T>

          \param b The shared pointer, which must not be empty.
        */
        object_ptr ( const shared_ptr<T> &b ) : shared_ptr<T> ( b ) {
                bdm_assert_debug ( this->get(), "object_ptr cannot be empty" );
        }

        /*! 
          Constructs an object_ptr that owns the pointer p. p must
          have been alllocated by new!
        */
        object_ptr ( T *p ) : shared_ptr<T> ( p ) {
                bdm_assert_debug ( p, "object_ptr cannot be empty" );
        }

        /*!
          \brief Assignment operator
        */
        object_ptr<T> &operator= ( const object_ptr<T> &other ) {
                shared_ptr<T>::operator= ( other );
                return *this;
        }
};

#define SHAREDPTR(class_name) typedef bdm::object_ptr< class_name > class_name##_ptr

#define SHAREDPTR2(template_class_name, template_parameter_name) typedef bdm::object_ptr< template_class_name < template_parameter_name > > template_class_name##_##template_parameter_name##_ptr

}

#endif